I inherited a bike with an Eddy Merckx frame about a year ago. The bike has some Campagnolo components, including rear shifters which have an issue. I'd rather repair the shifter than replace it because the bike as some sentimental value, and the longer I can go without replacing parts the better.

The thumb shifter usually locks when I try to shift, but if I hold the brake lever over to the right with my index finger the thumb shifter functions again. My mechanic told me that a spring in the shifter needs to be replaced and that it can be hard to identify a compatible spring.

Can anyone tell me what model these shifters are so I can dig up some information on them? Or, even better, does anyone have any experience with this issue and a possible fix?